Objective To study the relationship between chlamydia pneumoniae and coronary heart disease.Methods Serology and PCR for detecting chlamydia pneumoniae were conducted in groups of non coronary heart disease(NCHD),stable angina pectoris(SAP),unstable angina pectoris(UAP)and acute angina pectoris(SAP),unstable angina pectoris(UAP)and acute myocardial infarction(AMI).Results No significant difference was found in serology among each group.The positive rate of PCR of CHD group was higher than that of CHD group,and the positive rates of PCR of both UAP and AMI were higher than that of SAP group.There was no significant difference between the positive rates of PCR of UAP and AMI group.Conclusion Chlamydia pneumoniae contributes to the formation of coronary heart disease and the ustability of plaque.